Conventionally, a purification operation by adsorption, such as recovering a valuable substance such as a protein by adsorption or removing impurities by adsorption, performed in a bioprocess, such as a pharmaceutical product production process, has been performed by passing a solution to be treated through a column charged with porous gel beads having a particle size beyond 100 μm and serving as an adsorbent. As the gel beads, beads formed of a polysaccharide such as cellulose, dextran and agarose are frequently used. These beads which are porous beads, have numeral micropores within a bead particle, and the beads acquire a capacity of adsorbing a desired substance by increasing a specific surface area by providing micropores. A crude-material solution, which contains a desired substance and impurities and obtained by e.g., cultivating, is passed through the column charged with the porous gel beads and the desired substance or impurities are separated by being adsorbed by a functional group having protein adsorption ability and immobilized to the micro pore surface when the solution passes through the micropores. However, conventional gel beads have a problem. A large resistance is offered to the migration of a substance into a gel bead particle, more specifically, to the diffusion of a substance through the micropores. Therefore, as the loading speed of a crude-material solution to a column increases, a functional group within micropores is not used for adsorption and only the functional group present on the outer surface of the gel bead particles are used for adsorption. As a result, an adsorption capacity greatly decreases. Purification by adsorption is not easily performed at a high speed.
On the other hand, gel beads formed of nonporous particles, in which only a functional group immobilized to the outer surface of the particles functions, have an advantage in that even if a loading speed of a liquid increases, a decrease of adsorption capacity is low. However, since the absolute value of the specific surface area of such gel beads is small, the adsorption capacity sufficient for industrial use is not easily obtained, and use of the gel beads mostly remains for analysis.
Furthermore, studies have been conducted on a method, in which a functional group is immobilized to a micropore surface of a porous membrane such as a micro filter and a solution to be treated is forcibly passed through micropores by filtration (see, for example, Non-Patent Documents 1 and 2). According to the method, even if a solution is loaded at a high speed, the functional group within a micropore can be efficiently used. Thus, a decrease of adsorption capacity rarely occurs.
Non-Patent Document 1: Kyoichi Saito et al., “Chemical Engineering”, August issue, 1996, pp. 25-28
Non-Patent Document 2: Noboru Kubota, “Radiation and Industry”, December, 1998, No. 80, pp. 45-47